Wednesday, 20 November 2013

Diet is an IQ test

It may be a hazard of working in a medical school, but from time to time I have felt the need, on the basis of some apparently valid research, to change my diet somewhat. At one stage that involved eating more fibre (unpleasant results and unnecessary investigations) eating much more fruit (same, plus higher bills) reducing the amount of red meat and bacon (increased gloom, slightly lower bills), taking and not taking vitamins, and other similar variations.

Come to think of it, I was probably responding to the media rather than any of my colleagues, since no-one in the staff dining room took any notice of such things. It was also there that I learned the basic metabolic formulas which revealed that humans are efficient and burn relatively few calories in normal daily activities, so if you want to keep slim you have to reduce your food intake. The key to avoiding being fat was: Eat less.

I have tried to cover these issues in a previous post “Fat is an intellectual issue”

If a good diet leads to good health, then any person of normal intellect should be able to work out what is required to maximise their chance of a healthy and long life. In modern life, working out what to eat is an IQ test.

With a title like that, the paper is riding for a fall. I cast a belligerent eye on this 20 author publication, expecting the worst. They condemn, for lack of evidence, the following myths (beliefs held to be true despite substantial refuting evidence):

4) It is important to assess the stage of change or diet readiness in order to help patients who request weight-loss treatment.

5) Physical-education classes, in their current form, play an important role in reducing or preventing childhood obesity.

6) Breast-feeding is protective against obesity.

7) A bout of sexual activity burns 100 to 300 kcal for each participant.

In deference to those of my readers who cannot read the whole paper because they are about to have sexual intercourse: in reality it burns only about 14 calories more than watching television, apparently.

Anyway, all 7 of these claims have been refuted by reasonable studies. Having got rid of 7 myths, they then tackle 6 presumptions (widely accepted beliefs that have neither been proved nor disproved):

So, eat less, though eating less is difficult, and in the US both drug companies and surgeons are after your money, some of which you can save by eating less in the first place.

They reflect: “When media coverage about obesity is extensive, many people appear to believe some myths simply because of repeated exposure to the claims.[] Fortunately, the scientific method and logical thinking offer ways to detect erroneous statements, acknowledge our uncertainty, and increase our knowledge. [] Moreover, we often settle for data generated with the use of inadequate methods in situations in which inferentially stronger study designs, including quasi-experiments and true randomized experiments are possible. In addition, eliminating the distortions of scientific information that sometimes occur with public health advocacy would reduce the propagation of misinformation.”

My preliminary impression is that I warm to these authors, all 20 of them, when they are knocking down the myths and presumptions, but I think they pull their punches on the facts section. They stress that wanting to go on a diet and being told to go on a diet doesn’t usually result in the sustained maintenance of the diet. Fine, but we are talking about obesity. They note that “energy reduction is the ultimate dietary intervention” and that nothing else works unless “accompanied by an overall reduction in energy intake”. The English for that is: “Eat less”. Pity they put it as Fact 2, and buried it somewhat as an implication. Get that fact in your mind and you will have no need for surgeons. The way the authors handle it, that crucial fact has little impact. I cooled to them at the end. They started well, and then petered out.

Next up is Prof David Colquhoun, who focuses his sceptical eye on the broad range of diet claims and briskly asserts: We know little about the effect of diet on health. That’s why so much is written about it.

First off, Colquhoun draws attention to the long list of conflict of interests listed by the Casazza paper authors above, including many food manufacturers, which he says complicates an already messy field. He goes on to quote with great approval a paper BMJ 2013;347:f6698 doi: 10.1136/bmj.f6698 (Published 14 November 2013) by John Ioannidis. I will summarise the main points of the suggested references, with additional comments.

Most nutritional studies are observational, not experimental, and depend on questionnaires. There is always a nagging doubt as to whether every bacon sandwich and slice of chocolate cake will be faithfully reported, under the strain of recalling in vivid detail every lightly boiled cabbage and spoonful of cottage cheese.

Epidemiologists sometimes forget that people differ. Some are compliant boy scouts, some irresponsible spirits who don’t return questionnaires or follow instructions. Humans differ in intelligence and personality, but these considerations do not normally darken the door of diet epidemiologists. As far as they are concerned, people are what they eat, or become so after a decade of imprudent gluttony. Indeed, the meme “you are what you eat” seems to have had a great impact, despite being demonstrably false. Curious, the power of ideas, even stupid ones.

Even when semi-controlled trials are carried out, there is no way to ensure compliance, fall out from trials is rife, and sometimes the comparison conditions have to be made palatable by being only slightly different from the local cuisine (such that the low fat option is 37% fat, not the usually recommended 10%).

Then come all the odd and implausible results, such as that those that suggest we can halve the burden of cancer with just a couple of servings a day of a single nutrient (insert your favourite health food here). Miracle claims of this sort circulate widely in peer reviewed journals.

The other gripe among the cognoscenti? You read it here first. The sample sizes are too small, not followed long enough, and with high levels of sample attrition. Whoever you are, you cannot get round sampling theory. Samples of about 70,000 followed until death (with a proper link to death registers) will be required to identify even a few general patterns in diet which might account for a 5-10% increase in risk. If the studies are to mean anything, IQ, personality, sociological and occupational variables will have to enter the mix, and participants will probably have to be paid to stick to the course, and put up with random visits of inspectors looking in the fridge and the medicine cabinet. Count me out. So, although these correct and worthy researchers want controlled studies, they are not going to get them. Liberty will triumph over the food police.

After much thinking about how we can ever prove causality between diet and health, Colquhoun concludes that the only thing we can say at the moment with the remotest level of confidence about diet is:

Don’t each too much, and don’t eat all the same thing.

In shorter words, eat less.

That advice should be clear to all levels of intellect.

Disclaimer: Dinner was a microwaved Indian meal with curried chicken Madras 163, rice 269, potato cauliflower spinach 147, and nan bread 138, so a total of 717 calories, and then there was a large portion of home-made apple crumble and yoghurt. So, as the labels prove, a total of 717 calories.

14 comments:

A correlation between weight and IQ in industrialized nations would not be surprising, if only as a result of the apparent correlation between weight and SES. Has anyone ever tried to determine if such a correlation exists? (This strikes me as the kind of thing Herrnstein & Murray would have touched on in The Bell Curve, but I forget whether they did.)

"If a good diet leads to good health, then any person of normal intellect should be able to work out what is required to maximise their chance of a healthy and long life. In modern life, working out what to eat is an IQ test."

On the other hand, studies of IQ and alcohol consumption do not appear to support the higher-IQ --> healthy-habits connection. E.g., http://www.psychologytoday.com/blog/the-scientific-fundamentalist/201010/why-intelligent-people-drink-more-alcohol

You did: http://www.drjamesthompson.blogspot.co.uk/2013/01/what-makes-good-iq-story.html

Looking up by date is easier than searching.

IIRC Geoffrey Miller tweeted that the study did indeed find a general factor if you did some simple statistical adjustment (rotation something something?) Unfortunately I have only a superficial understanding of factor analysis. Any takers?

Btw, that g is not unitary at the brain/biological level has been understood by "g-men" for a long time. Quoting Meng Hu quoting Jensen's "The g-factor":

"it also fails to understand the nature of g. Here’s a passage of Jensen’s 1998 book, The g Factor (here), pages 130-132, about the unity of g and the concept of modular abilities, which is what your are referring to.

The g factor, which is needed theoretically to account for the positive correlations between all tests, is necessarily unitary only within the domain of factor analysis. But the brain mechanisms or processes responsible for the fact that individual differences in a variety of abilities are positively correlated, giving rise to g, need not be unitary. … Some modules may be reflected in the primary factors; but there are other modules that do not show up as factors, such as the ability to acquire language, quick recognition memory for human faces, and three-dimensional space perception, because individual differences among normal persons are too slight for these virtually universal abilities to emerge as factors, or sources of variance. This makes them no less real or important. Modules are distinct, innate brain structures that have developed in the course of human evolution. They are especially characterized by the various ways that information or knowledge is represented by the neural activity of the brain. The main modules thus are linguistic (verbal/auditory/lexical/semantic), visuospatial, object recognition, numerical-mathematical, musical, and kinesthetic. …

In contrast, there are persons whose tested general level of ability is within the normal range, yet who, because of a localized brain lesion, show a severe deficiency in some particular ability, such as face recognition, receptive or expressive language dysfunctions (aphasia), or inability to form long-term memories of events. Again, modularity is evidenced by the fact that these functional deficiencies are quite isolated from the person’s total repertoire of abilities. Even in persons with a normally intact brain, a module’s efficiency can be narrowly enhanced through extensive experience and practice in the particular domain served by the module.

Elsewhere, he notes, pages 259-261 :

But at some level of analysis of the processes correlated with g it will certainly be found that more than a single process is responsible for g, whether these processes are at the level of the processes measured by elementary cognitive tasks, or at the level of neurophysiological processes, or even at the molecular level of neural activity. If successful performance on every complex mental test involves, let us say, two distinct, uncorrelated processes, A and B (which are distinguishable and measurable at some less complex level than that of the said tests) in addition to any other processes that are specific to each test or common only to certain groups of tests, then in a factor analysis all tests containing A and B will be loaded on a general factor. At this level of analysis, this general factor will forever appear unitary, although it is actually the result of two separate processes, A and B. … However, the fact that g has all the characteristics of a polygenic trait (with a substantial component of nongenetic variance) and is correlated with a number of complexly determined aspects of brain anatomy and physiology, as indicated in Chapter 6, makes it highly probable that g, though unitary at a psychometric level of analysis, is not unitary at a biological level."

Factor analysis made simple. Principle components analysis is the best, because it follows simple mathematical processes and derives the latent variables mechanistically. It should work the same way every time. The only conceptual problem is that it is very strict, and sometimes misses an obvious (to the naked eye) secondary or tertiary factor. Factor analysis is more flexible, and more contentious, because you can rotate a factor in variable space in order to make it line up with an obvious constellation of tests. This is not a trick, because by doing so you might line up a second factor so that it makes sense at the cost of throwing out the next stage, and making the third factor a less good fit. So, a lot of work is done trying to justify a particular rotation of factors so that the explanatory factors line up with some conceptual dimension as neatly as possible. And that is just if you keep the factors orthogonal (at right angles to each other). Some treatments allow oblique factors. Think of it this way: longitude and latitude are locational factors, and they work well to identify places on earth. However, if you found that one particular line of longitude lined up with a lot of airports in almost a straight line across the world, you might be justified in giving that line of longitude prominence, simply because it simplified calculating airport time zones.